1. Field of the Invention
This invention relates to a process for the preparation of substantially crystalline calcium sodium metaphosphate. More particularly, this invention relates to a dry mix process for the preparation of substantially crystalline calcium sodium metaphosphate. Such substantially crystalline calcium sodium metaphosphate is useful to prepare asbestiform crystalline calcium sodium metaphosphate fibers which are characterized by having the form or appearance of asbestos (principally chrysotile) and by exhibiting an aspect ratio of at least 10, preferably at least 50, and an average in diameter from about 0.5 micron (.mu.m) to about 20 .mu.m.
2. Discussion of the Prior Art
Calcium sodium metaphosphate having the formula CaNa(PO.sub.3).sub.3 is known, primarily identified as the completely crystalline form. In Russian Pat. No. 1,122,610, a method is described for the preparation of crystalline calcium sodium metaphosphate (referred to therein as sodium-calcium metaphosphate). The process consists of interacting phosphoric acid at a concentration of 30-56% P.sub.2 O.sub.5 in an amount sufficient to provide a 5-15% excess over the stoichiometrically required amount first with a calcium compound, followed by a sodium compound. The resulting reaction mixture is heated at a temperature from 350.degree.-500.degree. C. However, it generally has not been feasible to employ such a procedure to prepare substantially crystalline calcium sodium metaphosphate containing up to about 40% amorphous calcium sodium metaphosphate. One reason for this difficulty stems from the fact that the Russian procedure employs a two-step neutralization or reaction scheme, one to neutralize or react with the calcium compound and the other to neutralize or react with the sodium compound.
The procedural requirements associated with the employment of a two-step neutralization or reaction scheme, of necessity, are time-consuming and inconvenient. Accordingly, any economically feasible method which substantially reduces the time and number of steps involved in the reaction scheme, while at the same time affording an excellent yield of product, would be a decided advance in the calcium sodium metaphosphate art.